There is a general need for portable handheld inhalators. A common group of inhalators are those that deliver an aerosolized drug in a fixed unit dosage when an actuator is pressed, squeezed or pulled by the patient.
It has been found that such inhalators are not optimal in that the delivered drug is not always introduced effectively into the respiratory passages of the patient. The coordination between the inhalation and the triggering of the drug delivery is critical and introduces the risk of an untimely administration with respect to the breathing. In addition, the breathing cycle and strength differs between different patients which introduces another difficulty.
Therefore, breath actuated inhalators have been developed. Such inhalators are provided with some kind of device that is sensitive to an airflow. Thus, when the patient inhales through a mouthpiece of the device, the sensitive device triggers the distribution of the drug. The drug is delivered into the airflow, i.e. the patient's inhalation, to continue into the respiratory passages of the patient.
Such inhalators, wherein a fixed unit dosage is administered when the patient inhales, are known, for example through WO 92/09323.
However, even with such unit dosage inhalators it is possible that the pharmaceutics is not inhaled in the most effective way. Therefore, electromechanically actuated inhalators are known that monitors the inhaled air flow and opens and closes, respectively, a valve in response to the measured air flow, i.e. a continuous administration of the drug is obtained, the length of which is determined by the respective inhalation of the patient.
An example of such an inhalator is described in the U.S. Pat. No. 5,718,222. With reference to FIG. 17 of said patent, a formulation is contained in a container that is closed by a valve. When a control unit has received a signal from a flow sensor being connected to the mouthpiece of the device, thereby indicating that the patient is inhaling, an actuator opens the valve in response to a signal from the control unit. With the valve open, the formulation enters into a resonance cavity where it is excited by a vibrating electromechanical mechanism to force the formulation through a membrane. The formulation exits from the membrane in an aerosolized state to be inhaled by the patient.
In order to obtain an aerosolization with very small and well-defined droplets the membrane of the device according to U.S. Pat. No. 5,718,222 is a so called Rayleigh type membrane. The Rayleigh flow phenomena is well known within the art, and is for example described in Hydrodynamics, Horace H. Lamb, 6th edition, p. 472-475, Dover Publication, New York, 1945.
An example of a breath activated inhalator utilizing a Rayleigh type membrane is described in the patent U.S. Pat. No. 5,718,222 referred to above. According to this patent, a pressurised liquid is propelled through the membrane.
Thus, although the inhalator according to U.S. Pat. No. 5,718,222 addresses the problem of drug administration controlled by the breath of the patient, it requires an electromechanical arrangement. This is a disadvantage in many applications, where low cost and small size is desired. In addition thereto, the need for electric energy makes the device vulnerable under circumstances where new batteries or an external energy source are not obtainable.
Therefore, there still remains a need for an all-mechanic breath controlled inhalator for continuously administering a drug when the patient is inhaling above a predetermined flow rate. The term “all-mechanic” is not to be regarded as excluding electric or electronic means and parts which facilitates the use of the inhaler, such as for example electronic display means, means for electronically monitoring the inhalation quality.